1. Field of Invention
The present invention relates to a repair device for a memory, and more particularly, to a device that repairs the defective bit lines of the memory.
2. Description of the Related Art
With great advance of science and technology, the electronic products, such as computer, cell phone, digital camera or personal digital assistant (PDA), are the common equipments for human to process and record data in daily life. The memory plays an important role in the said electronic products. With regard to the computer, the data, such as drivers or application programs, are loaded to the memory for the central processing unit (CPU) to access and execute the data. The memory temporarily stores the data for accelerating the operation of the computer.
As known, the memory includes a plurality of memory cells with array arrangement. When a row address is decoded, a word line corresponding to the row address is asserted so as to turn on the memory cells in the word line. When a column address is decoded, the bit line(s) corresponding to the column address can be selected for reading data from the memory to the bus or writing data transmitted through the bus to the memory. If one of the bit lines is defective, the data may not be transmitted to the destination so that a repair method should be developed for increasing the yield of the memory.
The simple way to repair the memory is to replace the defective bit line with a dummy line. Nevertheless, every bit line corresponds to a certain address in the memory so that a combination logic unit is needed for addressing the dummy line, and the complex register transfer language (RTL) code for addressing the dummy line causes huge gate count after synthesized. Once the dummy line is addressed to replace the defective bit line, the dummy line can not be reused. The bus bandwidth determines the maximum data size that can be transmitted once, or namely, determines how many bit lines can be selected in once transmission period. If there are several defective bit lines and they are utilized for transmitting data in different transmission periods, the way to utilize the un-reused dummy line doesn't conform to cost-benefit.